Perl中的bless的理解

[xywang@mnsdev13:~]$ cat Person.pm 
#!/usr/bin/perl -w
package Person;
use strict;

sub sleep() {
       my ($self) = @_;
       my $name = $self->{"name"};

       print("$name is person, he is sleeping\n");
}

sub study() {
       my ($self) = @_;
       my $name = $self->{"name"};

       print("$name is person, he is studying\n");
}
return 1;



[xywang@mnsdev13:~]$ cat Dog.pm 
#!/usr/bin/perl -w
package Dog;
use strict;

sub sleep() {
       my ($self) = @_;
       my $name = $self->{"name"};

       print("$name is dog, he is sleeping\n");
}

sub bark() {
       my ($self) = @_;
       my $name = $self->{"name"};

       print("$name is dog, he is barking\n");
}

return 1;

[xywang@mnsdev13:~]$ cat bless.pl 
#!/usr/bin/perl
use strict;
use Person;
use Dog;

sub main()
{
       my $object = {"name" => "tom"};

       # 把"tom"变为人
       bless($object, "Person");
       $object->sleep();
       $object->study();

       # 把"tom"变成狗
       bless($object, "Dog");
       $object->sleep();
       $object->bark();

       # 再把"tom" 变成人
       bless($object, "Person");
       $object->sleep();
       $object->study();
}

&main();

[xywang@mnsdev13:~]$  ./bless.pl   
tom is person, he is sleeping
tom is person, he is studying
tom is dog, he is sleeping
tom is dog, he is barking
tom is person, he is sleeping
tom is person, he is studying

[xywang@mnsdev13:~]$ cat wrong_bless.pl  
#!/usr/bin/perl
use strict;
use Person;
use Dog;

sub main()
{
       my $object = {"name" => "tom"};

       #没有把类型信息和$object绑定，因此无法获知$object有sleep方法
       $object->sleep();
       $object->study();
}

&main();

[xywang@mnsdev13:~]$ ./wrong_bless.pl   
Can‘t call method "sleep" on unblessed reference at ./wrong_bless.pl line 11.